This invention relates to a method of making an interpenetrating network of waterborne polymers and the coating compositions produced from such interpenetrating networks. The invention involves coreacting a waterborne polyurethane component and a functionalized waterborne polymer component wherein the functional groups of the waterborne polymer react directly with the functional groups of the polyurethane component or react indirectly with the polyurethane component via the functional groups of the chain extender. Alternatively, the polyurethane component reacts with a chain extender and the functionalized waterborne polymer component independently reacts with a chain extender that may be the same or different than the chain extender which reacts with the polyurethane prepolymer to create an interpenetrating polymer network. Coatings produced from the interpenetrating networks of the present invention possess superior solvent resistance and film hardness and are particularly useful as high performance industrial coatings.
Other methods of producing interpenetrating polymer networks involve dispersing polymerizable monomers in a polyurethane dispersion and then polymerizing the monomers in the presence of the polyurethane. U.S. Pat. No. 4,198,330 discloses a method for making a stable aqueous dispersion of polymeric material which comprises: (a) producing an isocyanate-terminated polyurethane prepolymer in the presence of an inert liquid polymerizable ethylenically unsaturated monomer material as a solvent or diluent; (b) dispersing the resulting product in water; (c) chain-extending the prepolymer in the resulting aqueous dispersion; and (d) subjecting the resulting aqueous dispersion to vinyl addition polymerization conditions to polymerize the monomer material in-situ. The polymerizable ethylenically unsaturated monomers must be inert to the prepolymer-forming reaction; that is, they must be devoid of groups interfering with or reactive with the primary isocyanate and active hydrogen-containing reactants. Thus, the monomers should be devoid of --NCO groups and active hydrogen-containing groups such as --OH.
U.S. Pat. No. 4,730,021 discloses a process for preparing aqueous dispersion of urethane-acrylate graft copolymers comprising (a) reacting a polymerizable acrylate with a diisocyanate to produce a monoacrylated diisocyanate adduct; (b) reacting the adduct of (a) and other polyisocyanates with an organic compound containing at least one active hydrogen atom and a group which is capable of forming a salt group to form a prepolymer; (c) neutralizing the prepolymer and dispersing it in water, immediately followed by chain extending the prepolymer to obtain a chain extended acrylated urethane polymer dispersion.
U.S. Pat. No. 5,173,526 discloses a method for making an aqueous polyurethane-vinyl polymer dispersion which comprises: (a) forming a carboxy-containing, water dispersible, isocyanate terminated polyurethane prepolymer; (b) adding a vinyl monomer composition which includes a polyethylenically unsaturated monomer to the prepolymer/monomer mixture; (c) adding a tertiary amine to the prepolymer/monomer mixture; (d) dispersing the prepolymer/monomer mixture in water; (e) adding an oil soluble free radical initiator and a chain-extender to the aqueous dispersion; and (f) polymerizing the vinyl monomer and completing chain extension of the prepolymer by heating the aqueous dispersion. Suitable vinyl monomers include ethylenically-unsaturated hydrocarbons, esters and ethers, especially esters of acrylic and methacrylic acids, esters of vinyl alcohol and styrene.